The study is to test the density-pathology hypothesis within human populations, studied at the ecological level, within urban areas. We examine city blocks to minimize demographic and environmental heterogeneity within units of analysis. We have prepared city block data files on two large cities, San Diego (n equals 6,792) and Cleveland (n equals 6,073), and one smaller one, Peoria. Statistically, the small units prevent inflation of correlations due to aggregation effects. Density is only one measure of population distribution and we also study population potential, which better measures potential contact, which is central to sociological reasoning concerning the possible effects of density. We are also studying the components of density, particularly housing occupancy (persons per room), using alternative bases. During the project period we propose: 1. To complete the analysis of the data sets representing the two large cities; 2. To incorporate environmental variables through the use of aerial photographs; 3. To collect data on two additional large cities; 4. To study two cities in the largest size range at the tract level with a greater selection of pathology indicators, particularly morbidity. We have already collected data on Los Angeles. We are pursuing data on "stress-related" and contagious diseases. One methodological goal is to estimate aggregation effects, comparing tract and block analysis. A major theoretical goal is to develop an ecological conceptualization of the urban residential area and the density-pathology issue.